Tire pressure monitoring systems (“TPMS”) for vehicles are known in the prior art. A TPMS provides constant monitoring of tire inflation levels in all four tires of a vehicle, and a typical TPMS makes the tire inflation data available to the driver. A sensor/transmitter unit mounted on each wheel rim periodically transmits a signal conveying tire pressure information at a specified frequency to a receiver mounted elsewhere onboard the vehicle. The sensor/transmitter unit is a combination of an air pressure sensor and a radio frequency (“RF”) transmitter that encodes data in a manner suitable for RF broadcasting. The receiver, which is usually located in the passenger compartment, can be integrated with (or connected to) an in-dash TPMS processor that alerts the driver if tire pressure is too low. Conventional TPMS systems are disclosed in U.S. Pat. Nos. 6,507,276, 6,535,116, 6,581,449, and 6,400,263.
In automobile deployments, there are little if any direct RF signal paths between the sensor/transmitters and the TPMS receiver due to the metal composition of the chassis. Furthermore, the sensor/transmitters and the receiver are typically mounted in close proximity to conductive metal portions of the automobile. Consequently, the body of the vehicle causes electromagnetic field scattering that can adversely impact the operating signal strength range of the TPMS, resulting in undesired deep fading in the communication link between the sensor/transmitters and the receiver. Unfortunately, increasing the RF transmit power of the TPMS signals is not a practical solution because the maximum transmit power is limited by strict government regulations. Relocating the TPMS receiver to increase received signal strength is also not a practical solution due to the existence of complex wiring harnesses in modern automobiles.
Accordingly, it is desirable to have a TPMS having improved dynamic range compared to conventional TMPSs. In addition, it is desirable to have an onboard wireless communication system for vehicle applications, where wireless signal losses between the RF transmitter and the RF receiver are reduced. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.